Through a combination of genetic engineering and modern electronics (with a dash of nanotech), enhance plants to provide a host of services.

Imagine a tree where every leaf can vibrate in response to a signal: you now have a living speaker system. Strawberries, blueberries, oranges, apples could
be made to light up (bioluminescent plants have been proposed, but what if you want to turn off the light?). Turn a weeping willow into an outdoor air conditioner by having it pump heat from its leaves to its roots. You get the idea.

(Home:Garden was as close as I could come as there is no Product:Plant catagory)

Hadn't thought about until just now, but don't plants that move--Venus flytrap, bladderwort, sensitive plant--achieve motion by essentially hydraulic means rather than by tendons attached to contractile actuators? Point being, very fast and immediately reversible movements might not be achievable using plants' natural physiology.

Neat topic for speculative armchair engineering, though, phoenix. Plants' stringy vascular structures, like the strings in a celery stalk, might be adaptable as tendons--especially if one could convince the plant to double up, growing one tube that can slide inside another, like a bicycle cable in its sheath. And if we could coerce the plant into producing cells containing contractile polymers, pretty soon we'd have a true vegetable muscle system.

Your weeping-willow air conditioner is more likely, imho--I mean, lay down on a grassy lawn and the grass feels cool because it's doing some evaporative cooling already, losing liquid through its stomata. More like a swamp cooler than a heat pump, but hey it's getting close.

waugsqueke's right to cry wibni, perhaps, but...oh let's just play with it for a while?